A method is described of manufacturing shaped bodies, in particular fiberboard, chipboard or like boards, in which fibers, particles containing cellulose or particles containing lignocellulose are scattered with an admixed binder to form a mat and preheated before the mat is pressed to the shaped body, while supplying heat and pressure. Furthermore, the invention is directed to an apparatus for the manufacture of shaped bodies, in particular of fiberboard, chipboard, or like boards, in particular for carrying out the method of the present invention, comprising a scattering station, a forming line, a pressing station and a heating device inserted before the pressing station for the heating of a mat scattered by the scattering station onto the forming line prior to entry into the pressing station.
An apparatus of this kind, and also a corresponding method, are known from DE-PS 39 14 106. In the apparatus described in this document, the heating device is arranged in the region of the entry drum of the pressing station, in order, in this manner, to increase the output of shaped bodies, or to reduce the length of the press for a given output.
The disadvantage of such an apparatus is the fact that a relatively large quantity of thermal energy must be supplied to the mat, both in the heating device and also in the pressing station, and that the speed of transport of the mat may not exceed a certain maximum speed, because otherwise a complete heating of the mat over its full cross-section is not possible.
It is an object of the invention to so design a method and an apparatus of the initially named kind that the thermal energy to be supplied can be reduced with a uniform through-heating of the mat simultaneously being maintained. It is a further object to so further develop a method and an apparatus of the initially named kind that these can be used even more flexibly and in particular the output of shaped bodies can be increased or, with a given output, the length of the apparatus reduced.
The part of the object relating to the method is solved, starting from a method of the initially named kind, in that the preheating of the mat, consisting of the precompressed or pressed fibers or like particles, takes place by the supply of thermal energy from the interior of the mat outwardly to the surface of the mat. Correspondingly, the part of the object relating to the method is solved, in an apparatus of the initially named kind, in that the heating device is formed for the supply of heat from the interior of the mat outwardly towards the surface of the mat.
Thus, whereas the thermal energy of both the heating device and also of the pressing station is supplied in the arrangement of DE 39 14 106 from the outer sides of the mat in the direction towards the interior of the mat, the direction of supply of the thermal energy in the heating device in accordance with the invention is reversed.
Since the heat supplied to the mat in the pressing station via the press rollers takes place from the outer sides towards the interior of the mat, it is more favorable to already heat the interior of the mat in the preheating phase, whereas a heating of the outer sides is not so important. Through the combination of preheating from the inside towards the outside and a thermal treatment from the outside towards the inside within the pressing station, it is ensured that the mat is fully and uniformly heated over its entire cross-section.
Furthermore, the loss of the thermal energy supplied, which occurs on the path between the heating device and the pressing station, is significantly smaller when the mat has a xe2x80x9chot corexe2x80x9d than when the mat is heated via its outer sides in the heating device.
Accordingly, an energy saving can be achievedxe2x80x94on the one hand, since the mat does not have to be fully heated up to the outside in the heating device and, on the other hand, since the energy loss between the heating device and the pressing station can be reduced.
In accordance with an advantageous embodiment of the invention, at least one additive, in particular a catalyst for the binder contained in the mat, is also introduced into the mat from the interior of the mat outwardly to the surface of the mat.
An acceleration of the bonding process which takes place in the mat can be achieved by the supply of one or more additives, likewise from the interior of the mat outwardly to the surface of the mat. Due to the supply of the additives from the interior of the mat, the thickness of the mat to be penetrated is reduced so that a more uniform penetration of the mat by the additives is effected. Particularly the inner critical region of the mat is penetrated by the additives in an ideal manner in accordance with the invention.
The said object is further satisfied by two initially separate mats being scattered to form the mat, with these two separate mats being brought together such that the sides of the separate mats confronting one another form the interior of the mat and the sides of the separate mats remote from one another form the upper and lower sides of the mat respectively.
In accordance with the invention, two initially separate mats are generated which are brought together to form a single total mat. The sides of the separate mats contacting one another after the bringing together thus form the interior region and the sides remote from one another the upper and lower sides of the total mat. The two separate mats can thus be heated from their respectively confronting sides, which later form the inner region of the complete mat, by applying thermal energy from these sides toward the sides of the separate mats remote from one another.
The bringing together of the separate mats can be effected by a machine or also manually. For example, one of the separate mats can be transported on a transportation device designed, for example, as a conveyor belt, while the second mat can be manually placed from above onto the lower mat lying on the transportation device.
Instead of a separate scattering of two mats, in accordance with the invention a mat having a mat-like construction can be used which is cut up essentially parallel to its upper and lower sides, with the supply of heat taking place through the cut surfaces, both in the direction towards the upper side of the mat and also in the direction towards the lower side of the mat. For this purpose, a separating apparatus, which is in particular formed as a cutting apparatus, is preferably provided with which the mat can be divided into at least two part mats, in particular into an upper part mat and a lower part mat, with the heating device being arranged in the region between the part mats.
The part mats preferably have substantially the same thickness in this arrangement, so that a uniform through-heating of the mat is achieved from the inside to the outside, both to the upper side of the mat and also to the lower side of the mat. The heating device thereby advantageously lies directly against the cut surfaces of the part mats, since, in this way, an energy loss is largely avoided.
The separating apparatus is preferably formed as a saw, in particular as a band saw, and preferably as an endless band saw, with the cutting direction of the cutting apparatus expediently being directed opposite to the transport direction of the mat substantially parallel to the surface of the forming line. In this manner, a simple supply of the thermal energy is possible from the interior of the mat to the outside. Furthermore, the separation of the mat into two part mats can take place directly during the transport of the mat on the forming line in the direction of the press station without the transport process having to be interrupted or impaired in some other manner. Thus, the invention can be used both for the continuous manufacture of shaped bodies and also for the discrete manufacture of shaped bodies.
The mat is preferably prepressed prior to the preheating, since, in this manner, a tearing apart or falling apart of the fiber components of the mat is avoided during the cutting process. Furthermore, the invention is preferably used with mats which are made of fibers and not, for example, of shavings, since fibers mat together during the prepressing and thus endow the mat with a strength which is advantageous for the subsequent cutting process.
In accordance with a further advantageous embodiment of the invention the heating device includes a heating chamber which extends substantially over the full width of the mat and which has, in its regions confronting the part mats, in each case outlet openings, in particular slot-like outlet openings, for the dispensing of the heating medium, in particular of steam, from the heating chamber into the mat.
The preheating of the mat over its entire width can be carried out very simply and uniformly by the heating chamber. Furthermore, the outlet openings can be made at least partly closeable, in particular via a slider element, so that both a control of the quantity of the emerging heating medium as well as the location at which the heating medium emerges within the mat can be adjusted.
Advantageously, the heating device should be provided as close as possible to the entry to the press so that both the heat supply and, optionally, the introduction of the additives into the mat are effected directly prior to its entering into the nip.
It is furthermore possible to cut the mat asymmetrically, that is, into part mats of varying thickness, or correspondingly to bring together part mats scattered with different thicknesses into one uniform mat. It is furthermore possible to generate not only two, but a plurality of part mats, with these having different or identical thicknesses.
To reduce the friction between the part mats and the heating device, an oscillating device can be provided in accordance with the invention or the heating apparatus can be set into oscillation. The heating device can advantageously be coated, in particular at its contact points to the part mats, with thermal insulating material, for example with Teflon or the like. In this way, a premature curing or tendency to cure of the binder contained in the mat material can be avoided. The heating device can also contain, for example, sections, in particular chambers with a cooling medium, for example cooled air, instead of or in addition to insulating material.
A heating device designed in accordance with the invention can also be designed for the supply of thermal energy and/or additives in the opposite direction, i.e. from the exterior of the mat to its interior. Instead of supplying the heating medium and/or the additives via the openings of the heating device provided, for example, at the side, a vacuum can be generated at these openings, for example by the connection of a vacuum apparatus. By means of the vacuum generated in this way within the heating device, a heating medium and/or corresponding additives can be supplied to the upper side and/or lower side of the mat, whereupon they are conveyed through the respective part mat from the exterior to the interior of the mat due to the vacuum.
The invention will be explained in more detail in the following with reference to an embodiment and to the drawings.